1. Field of the Invention
The present invention relates to a mat, a holding sealing material, a method for producing a mat, and an exhaust gas purifying apparatus.
2. Discussion of the Background
Conventionally known mats include nonwoven fabric-like mats made from compressed inorganic fibrous materials such as fibrous silica or fibrous alumina. These nonwoven fabric-like mats are excellent in characteristics such as heat resistance and elasticity (repulsive force), and thus they are used for various applications.
For example, such a nonwoven fabric-like mat is used as a component of an exhaust gas purifying apparatus. Specifically, a typical exhaust gas purifying apparatus comprises a cylindrical exhaust gas treating body, a cylindrical casing which accommodates the exhaust gas treating body, and a mat-shaped holding sealing material disposed between the exhaust gas treating body and the casing, and the nonwoven fabric-like mat is used as a material for this holding sealing material. The holding sealing material is produced through steps such as a step of cutting a nonwoven fabric-like mat into a predetermined shape.
The holding sealing material which comprises a nonwoven fabric-like mat having repulsive force has a predetermined holding force. Thus, in the exhaust gas purifying apparatus, the holding sealing material securely holds the exhaust gas treating body at a predetermined position inside the casing. Further, since the holding sealing material is disposed between the exhaust gas treating body and the casing, the exhaust gas treating body is less likely to be in contact with the casing even if vibration or the like is applied, and exhaust gas is less likely to leak from between the exhaust gas treating body and the casing.
The exhaust gas purifying apparatus comprising a holding sealing material may be produced by stuffing an exhaust gas treating body wrapped with a holding sealing material into a casing.
Specifically, a holding sealing material is wrapped around the periphery of a cylindrical exhaust gas treating body to prepare a wrapped member, and the wrapped member is slide-inserted into a cylindrical casing whose inner diameter is smaller than the outer diameter of the wrapped member while the holding sealing material is compressed.
In this production method, therefore, the holding sealing material wrapped around the exhaust gas treating body is required to have an appropriately low height (volume) so that the wrapped member is easily stuffed.
Further, a high shearing force is applied to the holding sealing material when the holding sealing material is stuffed into the casing. Thus, the holding sealing material is required to have a certain degree of strength (hereinafter, also referred to simply as shear strength) so as not to be torn due to the shearing force.
JP-A 2006-207393 and JP-A 2007-127112 each disclose a conventional nonwoven fabric-like mat comprising an inorganic fibrous substance. These conventional nonwoven fabric-like mats are produced as follows: a fibrous alumina precursor, which is to be converted into an inorganic fibrous substance by firing, is compressed to prepare a sheet; multiple needles with barbs are inserted into/extracted from the sheet in the thickness direction of the sheet to prepare a needled sheet with multiple intertwined portions formed therein; and the needled sheet is fired.
The produced nonwoven fabric-like mat is cut into a predetermined shape, and thereby a holding sealing material is produced.
The contents of JP-A 2006-207393 and JP-A 2007-127112 are incorporated herein by reference in their entirety.